Printed circuit (PC) boards have found increasing application in electrical and electronic equipment of all kinds. The electrical circuits formed on these PC boards, like larger scale, conventional electrical circuits, need protection against electrical overloads. In particular, circuit boards and other electrical circuits within the telecommunications industry need protection against electrical overload. This protection can be provided by subminiature fuses that are physically secured to the PC board.
One example of such a subminiature, surface-mount fuse is disclosed in U.S. Pat. No. 5,166,656 (the "'656 patent"). The fusible link of this surface-mount fuse is covered with a three layer composite which includes a passivation layer, an insulating cover, and an epoxy layer to bond the passivation layer to the insulating cover. See '656 patent, column 6, lines 4-7. Typically, the passivation layer is either chemically vapor-deposited silica or a thick layer of printed glass. See '656 patent, column 3, lines 39-41. The insulating cover may be a glass cover. See '656 patent, column 4, lines 43-46. The fuse from the '656 patent has three layers protecting its fusible link. In addition, the fuse from the '656 patent has relatively thick glass covering. There are several other features in the '656 patent fuse which are unnecessary in the present invention.
One additional previous fuse is disclosed in European Patent Application No. 270,954. This "chip-type" fuse includes a conducting member 3 and electrodes 4a and 4b that wrap around an insulating member. The electrodes are not unitary with the conducting member, however, and the connection to the circuit board takes place on the lower surface of the substrate. In addition, several steps are required to create the electrodes. Furthermore, the protecting member is spread across the entire upper surface of the fuse. This fuse includes several other disadvantages.
The present invention is designed to solve these and other problems.